You might want to check out iLounge’s comprehensive list of 63 iPhone accessories, complete with links to product summaries for each one.
Be aware, however, that some accessories may not work as expected with the iPhone. iLounge’s Jeremy Horwitz warns that iPod speakers dubbed “iPhone-compatible” may be vulnerable to interference caused by the cell phone signal, and certain chargers could break when connected to the iPhone.
I’ll add that, although Apple has released the dimensions of the iPhone, some cases may not fit just right, so it might be worth waiting until after the 29th to buy your accessories.